The specific aim of this research is to study, in the monkey, secondary vestibular fibers ascending in the brain stem and primary and secondary vestibular fibers projecting to parts of the cerebellum. It is planned to produce discrete lesions in individual vestibular nuclei, in the medial longitudinal fasciculus and in the accessory oculomotor nuclei and to study the resulting degeneration by silver impregnation methods and by electron microscopy. Lesions in the vestibular ganglia and nerve will be used to study primary vestibular fibers passing to specific parts of the cerebellum. Degeneration will be studied by EM technics. Lesions in localized portions of the inferior and medial vestibular nuclei will be used to study secondary vestibular projections to the cerebellum. EM studies of secondary vestibulocerebellar fibers will be guided by the results of light microscopic investigations. It is intended to inject tritiated amino acids into individual vestibular nuclei and by autoradiographic technics trace the label transmitted to axon terminals by axoplasmic flow. Bibliographic references: Pierson, R.C. and Carpenter, M.B. 1974. Anatomical analysis of pupillary reflex pathways in the rhesus monkey. J. Comp. Neurol., 158:121-144.